Depositing was a concept that HGVC has had for some time now. The decision to deposit must be made the year prior to the grant year of the points. In other words, to deposit 2009 points into 2010, this action must be taken in 2008.
Rescuing is a new option offered just a couple years ago. This option allows you to take points from your current year and "rescue" the unused points into the following year. For example, 2008's left over points can be put into 2009. Before this option was introduced, if you didn't use your current years points, you would lose it....
Both methods require you to use the points that were moved foward to be used in the year it was moved into. These points can't be once again, moved forward. In addition, you are able to borrow points from the up coming year without cost...
Yes, both methods are a bit redundant. I think if you know for sure you have no use for next years points, you might want to deposit it to not have to worry about it. Then if you have need for it next year, you can always borrow it... So in 2008, you decide you don't need 2009's points. You deposit it into 2010. Then in 2009, you decide you do what to use some points, you can borrow it back with no cost...
There are those that deposit a bunch of points and then always borrow from the following year to allow one to use more points each year then they own. So let's say you have 5000 point contract in 2009. You deposit it into 2010. Then in 2009, you can use 7000 points and then deposit the remaining 3000 points (which are not technically, 2009 points) into the 2011 and then do it again in 2010 leaving you 1000 points which again can be moved forward and ... Yes, you eventually will run low on points which means you take a one year break and then do it again...